CCL: Reply for question regarding DlPoly free energy calcs along z-coord

 Sent to CCL by: "Wojciech  Gren" [wjgren|,|]
 If you need to fix one of the atom coordinates in DlPoly, the best place is
 freeze subroutine, which deal with fixed atoms. The modification could be to
 make zero all velocities and forces in z-direction, and record the forces. We
 use similar method but developed it to be able also apply force to particular
 group of atoms and use any directions.